Climate Change 101: An Introduction

By Joseph Romm, PH.D.

Climate change is real. It is human-caused. We’re seeing the effects now.

And unless we start cutting carbon pollution soon, the impacts threaten to destroy the stable climate that made modern civilization possible. Let’s take these well-established points in turn.

HOW GREENHOUSE GASES CHANGE THE CLIMATE

The greenhouse effect has made the life we know possible. The basic physics has been understood for over a century. The sun’s light warms the earth, which reradiates that heat as infrared radiation. Some naturally occurring atmospheric gases, including water and carbon dioxide (CO2), let visible light pass through while trapping certain types of infrared radiation.

These heat-trapping greenhouse gases act as a partial blanket that helps keep the planet about 60°F warmer than it otherwise would be — which is ideal for us humans and the modern agricultural system we have created to feed billions of people. Since the dawn of the industrial revolution more than two centuries ago, however, humankind has been spewing vast quantities of extra greenhouse gases into the atmosphere, primarily from deforestation and burning fossil fuels—coal, oil, and natural gas.

The extra trapped heat has warmed the Earth about 1.5°F in the past century. “Warming of the climate system is unequivocal,” according to the September 2013 report from the world’s leading climate scientists that was endorsed by all of the 195 member countries of the Intergovernmental Panel on Climate Change (IPCC).1

The U.S. National Academy of Sciences said in 2010 the evidence for this warming is so strong it is a “settled fact.” 2

HOW WE KNOW RECENT WARMING IS HUMAN-CAUSED

How confident are we that humans are behind the warming? As the AP reported in September, “Top scientists from a variety of fields say they are about as certain that global warming is a real, man-made threat as they are that cigarettes kill.” 3

Some 97% of climate experts share the view that humans are changing the climate.4 Only the increase in manmade carbon pollution and the greenhouse effect can explain the rate and magnitude of recent surface temperature warming, the observed atmospheric profile of warming, the observed changes in ocean heat content, and the increased levels of atmospheric moisture — to name just a few of the human “fingerprints” on recent climate change.5

Significantly, all of the non-manmade sources of climate change – such as volcanoes and changes in the sun’s radiation or the Earth’s orbit — would be cooling the planet were it not for manmade global warming pollution.

That’s why the 2013 IPCC report said “the best estimate of the human-induced contribution to warming” since 1950 is that humans are responsible for all of it.

More than 150 recent studies document that we are seeing the effects of climate change now.6

Like a baseball player on steroids, our climate system is breaking records at an unnatural pace. And like a baseball player on steroids, it’s the wrong question to ask whether a given home run is “caused” by steroids. Home runs become longer and more common. Similarly climate change makes a variety of extreme weather events more intense and more likely.

MORE HEAT WAVES, DROUGHTS, FLOODS, WILDFIRES, AND MORE

Warming directly makes heat waves, longer, stronger and more frequent. For instance, a major 2012 study found that extreme heat waves in Texas, like the one that occurred in 2011, are much more likely — 20 times more likely in years like 2011 — to occur than they were 40-50 years ago.7

The warming directly makes droughts more intense by drying out and heating up land that is suffering from reduced precipitation. The warming also worsens droughts by causing earlier snowmelt, thus reducing a crucial reservoir used in the West during the dry summer season. Finally, climate change shifts precipitation patterns, causing semi-arid-regions to become parched, something scientists we spoke to said they are already observing in the Mediterranean and, apparently, the southwest. The 2012 Texas study found “indications of an increase in frequency of low seasonal precipitation totals.”

The heat and the drying and the early snow melt also drive worsening wildfires, particularly in the West. The wildfire season is already more than two months longer than it was just a few decades ago, and wildfires are much larger and more destructive.

Warming also puts more water vapor in the atmosphere, so that wet areas of the world become wetter and deluges become more intense and more frequent. This has already been documented and linked to human activity in the northern hemisphere. As NY Governor Andrew Cuomo said after his state was slammed by Superstorm Sandy just two years after it was deluged by hurricane Irene, ”We have a one-hundred year flood every two years now.”

And warming raises sea levels by heating up and expanding water – and by melting landlocked ice in places like Greenland and Antarctica. Those rising sea levels in turn make devastating storm surges more likely. For instance, warming-driven sea level rise nearly doubled the probability of a Sandy-level flood today as compared to 1950.

TODAY’S CLIMATE CHANGES ARE JUST THE TIP OF THE ICEBERG

Yet as much as we are already seeing serious impacts today, they are but the tip of the iceberg compared to what we face if we don’t start rapidly replacing fossil fuels with carbon-free sources of energy. Many studies project that on our current emissions path the planet will warm another 7°F to 10°F over the next hundred years.8

Here is what that would mean for the Earth’s climate after some 10,000 years of relatively stable temperatures:

CARBON POLLUTION SET TO END ERA OF STABLE CLIMATE

Such an unprecedented and rapid temperature change would have a devastating impact on the climate and our ability to feed 9 billion people post-2050. Places like Kansas would see temperature at or above 100°F for the entire summer by century’s end. Studies suggest large parts of the world’s currently habited and arable land would either be submerged or turned into a Dust Bowl (as in the case of the U.S. Southwest).9

The most destructive heat waves, droughts, and floods we suffer through today would be the norm. One study found that the Sandy-type storm surge that devastated much of the Jersey coast would be an every-year event in a half-century.10

“THE MOST FEARSOME WEAPON OF MASS DESTRUCTION”

On our current path of inaction, sea levels are projected to be as much as 3 to 6 feet higher by century’s end. Harold Wanless, chair of University of Miami’s geological sciences department, said last year, “I cannot envision southeastern Florida having many people at the end of this century.”11

And seas would keep rising some 5 to 10 inches (or more) each decade thereafter, until sea levels are 80 feet higher, and, eventually, when all the Earth’s ice has melted, more than 200 feet higher.

Large parts of the ocean would turn into hot, acidified dead pools, devoid of marine life. We could lose 50% or more of the Earth’s species. Entire ecosystems would collapse, and tropical diseases and invasive species would spread indiscriminately.

So you can understand why John Kerry called climate change “the world’s most fearsome weapon of mass destruction” in a February speech in Indonesia. And you can understand why so many scientists we talked to for our series “Years of Living Dangerously” are speaking out.12

As climatologist Lonnie Thompson said back in 2010, “Virtually all of us are now convinced that global warming poses a clear and present danger to civilization.”13

Joseph Romm, PH.D.

Chief Science Advisor

Joe Romm is a Fellow at American Progress and is the Founding Editor of Climate Progress. Romm was acting assistant secretary of energy for energy efficiency and renewable energy in 1997, where he oversaw $1 billion in R&D, demonstration, and deployment of low-carbon technology. He is a Senior Fellow at American Progress and holds a Ph.D. in physics from MIT.